.center-mixin{
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  top: 0;
}

//region triangle
.triangle-mixin(@_, @w, @c) {
  width: 0;
  height: 0;
  overflow: hidden;
}

/**
  尖头向左的三角形
 */
.triangle-mixin(L, @w:40px, @c:red) {
  border-width: @w;
  border-style: dashed solid dashed dashed;
  border-color: transparent @c transparent transparent;
}

/**
  尖头向右的三角形
 */
.triangle-mixin(R, @w:40px, @c:red) {
  border-width: @w;
  border-style: dashed dashed dashed solid;
  border-color: transparent transparent transparent @c;
}

/**
  尖头向下的三角形
 */
.triangle-mixin(D, @w:40px, @c:red) {
  border-width: @w;
  border-style: solid dashed dashed dashed;
  border-color: @c transparent transparent transparent;
}

/**
  尖头向上的三角形
 */
.triangle-mixin(U, @w:40px, @c:red) {
  border-width: @w;
  border-style: dashed dashed solid dashed;
  border-color: transparent transparent @c transparent;
}
//endregion